[clang] [clang][driver] Use platform specific calls to get the executable absolute path (PR #68091)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

You have failed tests on Linux CI:
```
Failed Tests (4):
  Clang :: Driver/mingw-sysroot.cpp
  Clang :: Driver/no-canonical-prefixes.c
  Clang :: Driver/program-path-priority.c
  Clang :: Driver/rocm-detect.hip
```
Windows CI has another test in Clang interpreter failing, but that might be not related to you.
You should be able to reproduce those test failures with `clang --build . -t check-clang-driver` (or `ninja check-clang-driver`).

https://github.com/llvm/llvm-project/pull/68091